Debashis Datta, Senior Manager (Civil & Structural), Institute for Steel Development & Growth, Kolkata.

The retrofitting becomes necessary to enhance the performance of structures including those encountered loss of strength due to deterioration or which have crossed their expected life. The success of retrofitting depends on the actual cause and the measures adopted to prevent its further deterioration. The process involves repair, retrofit, renovation and even part reconstruction.

Steel elements in the form of plates, channels, angles, I-sections along with anchor bolts / through bolts could be used with proficiency for retrofitting of a damaged RCC building. This paper has elaborated in detail different aspects of cracks developed in concrete structures with remedial retrofitting measures along with sketches and calculation methods. Some generic examples of retrofitting methodologies applicable to Global and / or Local failures in concrete have been cited in this paper. Along with the conventional measures of retrofitting some special measures / details using steel have also been discussed on case to case basis.

Use of steel profiled sheeting has been demonstrated to replace or retrofit a damaged concrete roof. Steel sections and sheets being lighter their use does not add extra dead load on the existing structure but offers strength to the structural element as well as system.

Detection and Prevention

Any structure needs periodic repairs and regular maintenance to continue its performance of withstanding the existing loads. But due to changing static as well as dynamic behavior of the applied loads, the structures undergo deterioration and ultimately loose material strength to develop cracks. In case of RCC structures, the cause of the failure could be known by studying the crack pattern and its depth, which helps in identification of cause and prescribing measures for repairs/retrofitting to enhance life expectancy of the structure.

The conventional design methodology ensures a life expectancy of an RCC building structure as about 70 years. But studies indicate that RCC structures develop deteriorating signals at half of structure life, demanding repairs / retrofitting / renovation. INSDAG had carried out one such study on the bridges of Indian railways, which establishes this fact by lots of examples all over India. Hence, it is necessary to understand the effective preventive measures against the development of cracks in RCC elements.

Global Symptoms and Local Symptoms

The structural behaviour and its failure mechanisms could be classified broadly as Global and Local based on the symptoms manifested in its failing members. If the redundancy of the structural system as a Global is high, the non-performance of a few members may not lead to the absolute failure of the structure unless redundancy reduces to zero. But the failure of main members may impair the Global system. It is easier to carry out retrofit on the structural elements, if it is confined to the Local one and does not affect the Global system of the structure.

During repair or retrofitting, care needs to be taken towards the release of residual stresses in the existing system by appropriately propping and supporting and the redistribution of the stresses due to the new system. The best method is to apply props and supports to structural members being repaired / retrofitted to get the residual stresses released. Even after the structure gets retrofitted, it is desirable to keep the props and supports in place for some time and remove them sequentially so that the new stress pattern in the structural element can be redistributed evenly without effecting any undue stress concentration at any point of time.

When the symptoms of failure lead the structure to a mechanism i.e. the state of failure, it requires additional props / supports to hold the system during the retrofitting activities. Even sometimes, it is required to renovate a part of the structure as a measure of retrofitting because that improves the health of the structure and increases its life expectancy.

Steel Elements Used in Retrofitting

Steel elements in the form of plates, channels, angles, I-sections along with anchor bolts / through bolts could be used for retrofitting a damaged RCC building. The detailing of the joints of Steel members with the cracked RCC members requires study of the nature of cracks, their extent and depth. Since, it is very easy to give the steel members different shapes, it could be detailed in the most favourable way to fit into the system according to its necessity and available spaces. Some specific failures and its retrofitting measures are explained below.

An RCC beam is prone to fail by either flexure and / or by shear force. The stressed zone for shear in the beam is located near the supports and cracks develop at an angle of 450 starting from the point of support. But the stressed area for the flexure is near the mid-span and its failure crack develops vertically.

This section of the article is only available for our subscribers. Please click here to subscribe to a subscription plan to view this part of the article.

High-rise buildings need special attention when it comes to waterproofing as the challenges inherent in them are peculiar in nature. Unfortunately, there is a lack of knowledge on the remedies and products available in the market as water- proofers continue to

Read more ...

The longevity of structures depends on how much resistance the building element will offer to water ingress. Water leakage not only reduces the durability but also hampers the serviceability or usability of the structure; hence, a good waterproofing system will

Read more ...

Terrace waterproofing is particularly important and is considered a priority as the roof is always exposed to harsh climatic conditions and weather changes. Rajeev Gupta, Business Head, ECMAS Construction Chemicals Pvt. Ltd. An effective waterproofing solution

Read more ...

Cement concrete is one of the most important construction materials and is practically basic to present-day developments. It is strong enough mechanically, yet vulnerable to deterioration. It thus gets damaged and even fails. This deterioration may be due to the weathering

Read more ...

Gradual shift in lifestyle has driven the idea of modern construction towards developing underground spaces and buried structures to bring efficiency in use of space. However, the improved efficiency comes with an increase in challenges like infiltration

Read more ...

Industry experts Kunjan Popat, General Secretary, Waterproofing Association of India; Ramendra Bahadur Sinha, Managing Director, Agrani Enterprises, and MS Sudish, Director, SIWIN Institute of Waterproofing and Insulation, share the challenges

Read more ...

Durability is a key requirement for modern infrastructure projects – highways and roads, bridges, airports and airfields, walkways and plazas, parking structures and stadiums. Miles of concrete must

Read more ...

Buildings have major environmental impacts over their entire life cycle. Resources such as ground cover, forests, water, and energy are depleted to give way to buildings. Today, India has demonstrated

Read more ...

Scour is a natural phenomenon caused by the erosive action of flowing stream on alluvial beds. Failure of bridge due to scour at their foundations, which in this case consisted of abutments and pier, one 1.2 dia

Read more ...

To protect concrete structures like Flyovers, Bridges, Parking areas, Big Commercial and Residential Buildings, the normal decorative exterior paint will not serve the purpose as these paints are not vapour permeable

Read more ...

Repair Strategy of Stoplog Sill Beams During Operation Stage of 510 MW Teesta-V Power Station in Sikkim Running Power Stations serve as a boom to the economy of the country and any generation loss due to construction

Read more ...

Concrete protective liner is a multipurpose solution for waterproofing and protection of concrete surfaces against corrosion and destruction. The product warranties long-term and reliable protection of structures

Read more ...

Sangeeta Pandey, Chief Manager (Civil), Power Grid Corporation of India Ltd., Patna, PVS Sudhakar, Sr. General Manager (Civil), NOFN Works, Power Grid Corporation of India Ltd., Vishakhapatnam & Dr. Achintya, Professor of Civil

Read more ...

Samir Surlaker, Director, Assess Build Chem Private Limited discusses some new joint treatments and injection systems in waterproofing. It is a myth that waterproofing treatments can be carried out by application of single material

Read more ...

Years of research plus decades of practical experience have enabled FAIRMATE to develop detailed solutions to restore and rehabilitate concrete structures with structural rehabilitation, retrofitting and strengthening of RCC structures

Read more ...

Sunny Surlaker, Head Technical Services, Assess Build Chem writes on the selection ideologies, materials and methods for defect remediation in Concrete Buildings. The building façade or the envelope is the primary line of

Read more ...

This article provides some basic information on effects of fire on concrete, various condition evaluation methods, and show findings from a case study of a fire exposed concrete foundation in California, and informs construction

Read more ...

There is considerable controversy within the concrete repair industry regarding the use of bonding agents as a pretreatment method for the repair of deteriorated concrete. This paper examines the use of bonding agents

Read more ...

This paper discusses the effects of fire on concrete and provides a methodology to assess, evaluate and repair concrete structures. Though concrete is among the best fire-resistant building materials, it does get damaged when

Read more ...

The ACI 562 Code Requirements for Assessment, Repair, and Rehabilitation of Concrete Structures and Commentary was first published in 2013 and revised in 2016. Development of ACI 562 was an industry response to variations

Read more ...

×
Sign-up for Free Subscription
'India Construction Week'
Weekly e-Newsletter on Construction Industry
Get the latest news, product launches, projects announced / awarded, government policies, investments, and expert views.
Click here to subscribe.